(1) Field of the Invention
This invention is directed to vertical stack (2,4,6 high) rolling mill stands used to roll out flat rolled metal products, particularly metals such as steel and aluminum, to a reduced gauge using a pair of work rolls that are between intermediate rolls, which in turn are between backup rolls. Vertical stack rolling mill stands include work rolls, and optionally, intermediate rolls and backup rolls. It is also directed to mills where the rolls are used for controlling the shape of the metal during rolling by applying significant bending forces on the roll ends.
(2) Description of Related Art
Currently, in the art, there is a need for improvement in roll bending design so that the bearing and hydraulic cylinder maintenance is lowered for a vertical stack rolling mill. Process needs for roll bending have caused higher bending forces with subsequent higher roll end deflections. Also, operating practices have changed which have caused the work rolls and intermediate rolls to be shifted perpendicular to the rolling direction for improved shape and edge performance, and these practices have raised important issues with regard to the placement of end bending forces. Current designs for work roll and intermediate roll chocks generally constrain them to vertical movement which causes the bearing raceways to pinch, gouge, or otherwise behave in ways that reduce the bearing life since the resultant force is not at the bearing center when the roll is shifted. There is also higher roll end maintenance when the ends have to be re-machined. Also, some current designs apply hydraulic forces in the positive bending direction only, which is less desirable.
Additionally, there is the need to provide for a rapid method of inserting rolls into the mill, which will also accommodate the need for a roll to be driven, but allow the use of a shifting mechanism to be the means by which the rolls are kept in the mill. In a typical, non-shifting mill arrangement, keeper plates are used to ‘lock in’ rolls into the mill window. In a shifting roll arrangement, it is important that the rolls maintain their engagement in the drive system at all times, and that the shifted position of the rolls is highly positive and precise.
Improved designs for inserting rolls into the mill without the need for electrically actuated clamping or lock in plates are of benefit if the rolls utilize a mechanical system rigid enough to hold the rolls in place during the rolling operation. There are production benefits to locking in rolls mechanically, rather than by a sequence of hydraulic/electronic actuators, due to the need to verify actual lock in and motion to ensure successful operation.
Others have worked on rolling mill designs. U.S. Pat. No. 4,537,057, for example, describes a six high rolling mill and certain features to reduce edge cracks in the sheet during rolling. FIGS. 4 and 5 in particular show improved mill window equipment and methods to apply rolling force to the metal strip work piece. The disclosed method, however, requires a large number of hydraulic cylinders to create the roll bending effect in the work roll and intermediate rolls, which causes maintenance issues and complicated control/operational problems. The bending effect ends up being applied to the work roll chocks less effectively, by use of a machined area in the chocks in a way that creates un-needed high stress points. The end result is that the work roll and intermediate roll chocks require a lot of machining, and therefore a high expense due to the complicated geometry required. Finally, the roll changing method is not described as to efficiency. Another patent, U.S. Pat. No. 7,004,002 has similar issues.
U.S. Pat. No. 4,744,235 incorporates push/pull hydraulic cylinders to provide backup roll and work roll bending forces. It also includes compact designs for the work roll and intermediate roll chocks. It includes complicated horizontal hydraulic cylinders to steady and clamp the work rolls into position which adds to maintenance and complicates the operation of the overall system. The roll bending design causes significant moments in the roll chocks as well as end rotations. There is no allowance for this in the design causing the hydraulic cylinders to carry the resultant stresses and therefore incur significant maintenance.
U.S. Pat. No. 7,086,264 describes a six high mill stand with rolls that are inserted into the mill with a release able connection using a clutch type arrangement. This type of arrangement is suitable for a rotating connection, but not adequate for a rapid connection where the rolls shift perpendicular to the rolling direction.
U.S. Pat. No. 4,369,646 describes a hydraulic keeper system where shiftable rolls are kept in a mill stand. However, the hydraulic means of actuation to keep the rolls connected to the shifting mechanism is a less desirable method due to the need for portable hydraulics, hoses, maintenance, etc.
These designs and attempts by others are lacking in important technical aspects, especially in light of current trends in the industry, and improvements in mill design to address these issues is greatly desirable.